Antenna nutation mechanism with polarization control



April 4, 1967 3,312,975

ANTENNA NUTATION MECHANISM WITH POLARIZATION CONTROL R. F. HUELSKAMP 5 Sheets-Sheet 1 ATTORNEY A ril 4, 1967 R. F. HUELSKAMP ANTENNA NUTATION MECHANISM WITH POLARIZATION CONTROL 5 Sheets-Sheet 2 Filed Aug. 20, 1963 INVENTOR RICHARD F. HUELSKAMP ATTORNEY p 1967 R. F. HUELSKAMP 3,312,975

ANTENNA NUTATION MECHANISM WITH POLARIZATION CONTROL Filed Aug. 20, 1963 I 5 Sheets-Sheet 5 INVENTOR.

RICHARD F. HUELSKAMP ATTORNEY Aprii 4, 1967 R. F. HUELSKAMP 3,312,975

ANTENNA NUTATION MECHANISM WITH POLARIZATION CONTROL INVENTOR.

RICHARD F. HU E LSKAMP ATTORNEY April 4, 1967 A R. F. HUELSKAMP 3,312,975

ANTENNA NUTATION MECHANISM WITH POLARIZATION CONTROL Filed Aug. 20, 1963 5 Sheets-Sheet 5 INVENTOR.

RICHARD F HUELSKAMP ATTORNEY United States Patent 3,312,975 ANTENNA NUTATION MECHANISM WITH POLARIZATION CONTROL Richard F. Huelslkamp, Los Altos, Calif., assignor to Sylvania Electric Products Inc., a corporation of Delaware Filed Aug. 20, 1963, Ser. No. 303,322 4 Claims. (Cl. 343760) This invention relates to an improved mechanism for nutating devices such as antennas and the like.

Satisfactory operation of linearly-polarized conical-scan antenna systems requires that the primary feed device be nutated about a reference axis. By nutation is meant the motion of the primary feed whose propagating axis rotates and transcri'bes a circle about a longitudinal reference axis while the orientation of its transverse axis remains fixed. Conventional nutating drive mechanisms employ epicyclic gear trains which are complex, require ,ence axis, during high speed nutation of the antenna for varying the antenna polarization without interrupting high speed operation of the antenna.

In accordance with the invention, the drive mechanism :comprises an inner housing rotatably mounted in hearings in an outer housing. A device to be nutated, such as a primary feed device for an antenna system, is mounted in bearings on the inner housing with the longitudinal axis of the device inclined at an angle to the longitudinal axis of the outer housing. When the inner housing rotates relative to the outer housing, the longitudinal axis of the feed device describes a conical surface about the longitudinal axis of the outer housing. The feed device is restrained from rotating about its axis (e.g. the

axis of propagation) by a flexible coupling which is connected to polarization adjustment means for selectively rotating the primary feed device about its longitudinal axis. A flexible transmission line extends through this coupling for connection to the primary feed device.

Counterweights on the inner housing dynamically balance the feed device for rotation at high speeds.

The foregoing and other objects of this invention will be better understood from the following description of a preferred embodiment theerof, reference being had to the accompanying drawings in which:

FIGURE 1 is a perspective view of an automatic tracking antenna of the type with which a nutating mechanism embodying this invention may be used;

FIGURES 2 and 3 are schematic drawings of the primary feed device, and the inner and outer housings and their bearing supports for two positions of the feed device relative to the longitudinal axis of the outer housing;

FIGURE 4 are schematic representations of front views of the primary feed device in four positions during nutation about the axis of the outer housing;

FIGURE 5 is a side elevation partly in section of the primary feed device and the nutating mechanism;

FIGURE 6 is a transverse section taken on line 6-6 of FIGURE 5;

FIGURE 8 is an enlarged detail of the bearing support between the inner and outer housing; and

FIGURE 9 is an enlarged longitudinal central section of the rear portion of the nutating drive mechanism.

A preferred embodiment of the invention is shown in the drawings and is described herein as part of a radio frequency antenna system in which the object being nutated is a primary feed device for the system. The principle of the invention may be extended to other objects and systems which require motion in the form of nutation, and therefore the primary feed device shown and described is given as an example of one of such objects.

Referring now to the drawings, an antenna system of the type which utilizes the nutating mechanism of this invention is shown in FIGURE 1 and comprises a paraboloidal reflector 1 and a primary feed device 2 mounted at the focal point of the reflector on a supporting boom 3. The focal axis F of reflector 1 is located above the boom 3 as shown. The propagating axis P of the primary feed device 2 intersects the focal axis F of the reflector at an angle p, as shown in FIGURE 1, so the electromagnetic wave energy is radiated by the feed device 2 toward portions of the reflector lying generally above the intersection G of the focal axis F with reflector 1. Feed device 2 is mechanically coupled to a nutating mechanism 4 which causes the beam of radiated energy from the feed device to nutate as it illuminates the reflector 1.

Reflector 1 is supported by a rigid framework 5 on a pedestal 6 for tracking movements in azimuth and elevation. The boom 3 is mechanically rigidly secured to the framework 5 below the point G on the reflector and is itself a bridge-like structure which supports the primary feed device 2 and nutating mechanism 4 with a minimum of vibration.

Specific reference being had to the schematic representations in FIGURES 2 and 3, nutating mechanism 4 comprises an inner housing 7 rotatably supported in an outer housing 8 by cylindrical bearings 9 and 10 for rotation about longitudinal axis CA. Feed device 2 is supported in inner housing 7 by bearings 11 and 12 and is restrained from rotation about its axis DA relative to the inner housing by a flexible coupling 14 which is connected to the feed device at 15 and to fixed point 16. Axis DA intersects the reference axis CA at point A to form acute angle CAD. A reference point 17 is shown in FIGURE 2 at the top of the feed aperture. Arrows 18 and 19 indicate the direction of rotation of the inner housing, which is clockwise when FIGURE 2 is viewed along axis CA from left to right. Lon-gitudinally spaced counterbalance weights 2% and 21 are mounted on inner housing 7 on the side of axis CA diametrically opposite from axis DA of primary feed device 2 for dynamically balancing the latter.

FIGURES la-4d, inclusive, are schematic representations of four poistions of primary feed device 2 and counterbalance 20 during the nutation cycle. Points C and D represent the longitudinal axes CA and DA, respectively.

Outer housing 8 is rigidly connected to supporting boom 3. A drive mechanism causes inner housing 7 to rotate within the outer housing 8; such as in a clockwise direction (as viewed in FIGURE 4). Rotation of inner housing 7 causes feed device 2 to move so that its offset axis DA generates a conical surface about axis CA. Flexible coupling 14 prevents the feed device from rotating about its own axis DA, and thus the feed device nutates in a clockwise direction (as viewed) about reference axis CA. This nutation is graphically represented in FIGURES 4a to 4d. With a linearly polarized feed device, as shown. the direction of polarization remains constant as indicated by the arrow in these figures.

Since inner housing 7 rotates about its own axis DA, a simple drive mechanism connected to it is sufficient to induce the notation. No rotary joints are required because feed device 2 does not rotate about its axis, and the radio frequency transmission line may be connected directly to the feed device. I

Referring now to FIGURES 5,-9, inclusive, the primary feed device 2 comprises a tapered ridged waveguide horn 24 (see FIGURE 6) embedded in' and filled with a rigid synthetic foam material 25 such as fiber reinforced polyurethane foam. This construction provides a feed device with minimum weight and high strength and rigidity. The foam material 25 on the outside of the horn 24 preferably has a stepped conical shape with a generally circular cross section as shown in FIGURE 6 to reduce wind loading effects and to simplify mounting of the device in the nutating structure. A dielectric lens 26 in the horn aperture serves to focus the electromagnetic wave energy propagated by the horn.

The feed device is supported on the forward end (as viewed) m of inner housing '7 by an outer ring 27 (see FIGURE 5) which extends outwardly and rearwardly from the outer surface of the feed device. Ring 27 has an inner cylindrical surface 28 (see FIGURE 7) with an axis coincident with axis DA and engageable with the outer race of bearings 11. The inner mounting surface 28 of outer ring 27 is conically shaped and is adapted to seat tightly in a fixed position on the similarly shaped outer'surface of the feed device. An inner ring 29 is bolted to the front end of the inner housing and has a cylindrical surface 30 which engages the inner race of bearings 11. The axis of surface 3 is also coincident with axis DA.

The rear bearing support for feed device 2 on inner housing '7 is shown in FIGURE 9 and comprises an annular flange 31 connected to and-projecting axially from the rear part of the feed horn. This flange 31 has a cylindrical surface 32 with an axis coincident with axis DA and engaging the inner race of rear bearings 12. Annular step 33 formed on the adjacent part of the inner housing has a cylindrical surface 34 coaxial with surface 32 and engaging the outer race of bearings 12.

The inner housing 7 preferably has a stepped conical shape which reduces from a maximum diameter at the front (to the left as viewed in FIGURE to a minimum diameter at the rear end. The outer housing 8 Within which the inner housing is mounted similarly has a stepped cylindrical configuration reducing from a maximum diameter at the front to a minimum diameter at the rear. The front portion of outer housing 8 has a radial mounting flange 35.

In order to support inner housing 7 within outer housing 8, a cylindrical surface 38 is formed on the exterior of the inner housing and is arranged to engage the inner race of bearing 9. Similarly, the front end of outer housing 8 has an inner cylindrical surface 39 which engages the outer race of bearing 9. Both of the housing surfaces 38 and 39 have axes coincident with axis CA. The rear .portion of the inner housing has a cylindrical surface 40, see FIGURE 9, which engages the inner race of bearing 10. A cylindrical surface 41 on the outer housing engages the outer race of this bearing. Both surfaces 40 and 41 have axes coincident with axis CA.

In order to dynamically balance the offset feed device, counterweight 20 is secured to a U-shaped member 42 which in turn is anchored to the inner housing by bolts 43 adjacent to front support bearing 9. Counterweight 20 rotates with the inner housing and is located with its center of gravity on the side of axis CA diametrically opposite from feed device axis DA. A rear counterweight 21 is similarly secured to the inner housing between front and rear bearings 9 and 10, respectively.

Inner housing 7 is rotated about axis CA by a motor 44 mounted on bracket 45 secured to front flange 35 4 of the outer housing 8. Motor 44 and a pinion 47 drive a belt 48 that frictionally engages a drive ring 49 on the inner housing. The axis of ring49 coincides with axis CA. Themating surfaces of belt 48 and drive ring 49 preferably are fluted to insure nonslip driving action.

In order to provide for transmission of radio frequency energy to and from the feed horn, a rigid fitting 50 (see FIGURE 9) is secured by bolts 51 to the annular flange 31 at the rear of the feed horn. Fitting 50 has a tubular hub 52 with an axis coincident with axis DA. A coaxial connector 53 from the feed horn is connected within hub 52 to an externally extending coaxial line 54, and a matching device 55 is provided at this connection.

The rear part (to the right as viewed in FIGURE 9) of hub 52 is connected to flexible coupling 14 which comprises longitudinally spaced rigid mounting collars 57 and 53 connected by a flexible sleeve 59 preferably made with helically wound wire or the like. The front collar 57 of the sleeve is non-rotatably' connected to hub 52.

Coaxial line 54 extends through collars 57 and 58 and sleeve 59 of coupling 14 and also through rigid straight sleeves 60 and 61. Sleeve 60 is non-rotatably secured to rear collar 58 of the flexible coupling. Sleeves 60 and 61 are secured together by bolts 62 and are both supported for rotary movement on the rear of outer housing 8 by an annular antifriction bearing 63 made of suitable material such as nylon. The bearing is secured to flange 64 on rear sleeve 61 and engages the adjacent inner surface of outer housing 8. Thus sleeves 60 and 61 are rotatable relative to outer housing 8 so as to induce corresponding rotary motion in feed device 2 through flexible coupling 14 and fitting 50 secured to the rear of the feed horn.

During rotation of the inner housing 7 by drive motor 44, the front collar 57 of coupling 14 follows the angular movement of entire feed device 2. Rear collar 58, however, is stationary. Flexible sleeve 59 permits this relative motion between the collars without, however, permitting the front collar 57 (and therefore the feed device 2) to rotate about the axis DA. In other words, flexible sleeve 59 restrains the entire feed device from rotating about its axis DA while the inner housing is rotating, and thus the nutating motion is derived.

An important feature of the invention is the provision for changing the angle of polarization of the feed device while the latter is nutating. This is accomplished by polarization control mechanism comprising a driven sprocket 66 secured to rear sleeve 61, a chain 67 associated with that sprocket, and a motor 68 and drive sprocket 69 for driving the chain. Motor 68 is supported on a bracket 70 secured to outer housing 8 as shown in FIG- URE 5. Through selective energization of motor 68 by local or remote control, sleeves 60 and 61 and coupling 14 are caused to rotate through a desired angle and thereby similarly cause the feed device 2 to rotate through the same angle about its axis DA. Coaxial line 54 is sufficiently torsionally flexible to accommodate changes in polarization angle normally required in operation, say from 0 degrees to degrees, and therefore no rotary joints are required in the mechanism.

In order to prevent damage to the coaxial line and associated connections as a, result of inadvertent or accidental continuous operation of the polarization control motor in one direction, a rotary joint may be added as indicated at 71.

r The actual polarization angle of the feed device is accurately determined by a synchronous transformer 72 having a shaft 73 connected by belt 74 to rear sleeve 61 of the mechanism. This transformer provides an elec-' trical readout of the actual angular displacement of the feed device.

In order to provide an electrical readout of the instantaneous angular position of the feed device about axis CA during the nutating cycle, a reference generator 76 mounted on outer housing bracket 77 is rotatably connected by its sheave 78 and belt 79 to the rear portion of the inner housing 7.

As modifications of this invention can be made without departing from its true spirit, the scope of this invention is to be determined from the appended claims.

What is claimed is:

1. Mechanism for nutating a Waveguide feed horn adapted to propagate electromagnetic waves comprising an outer housing, 7

an inner housing disposed within and having a forward portion projecting outwardly from one end of the outer housing,

antifriction bearings between said housings for supporting the inner housing for rotation about a first axis relative to the outer housing,

a motor operatively connected to the inner housing for rotating the latter about said first axis,

said feed horn being disposed Within and having a forward portion extending outwardly from the forward portion of the inner housing,

antifriction bearings between said feed horn and inner housing for supporting the horn for rotation about a second axis relative to the inner housing,

said axes being angularly related and intersecting at a point adjacent to the end of the horn opposite from the forward p-OItiOn thereof,

counterweight means connected to said inner housing on the side of said first axis diametrically opposite from the second axis,

tubular means connected to the rear end of the feed horn and extending rearwardly therefrom comprising a flexible sleeve and a rigid sleeve interconnected to the flexible sleeve,

a flexible coaxial line connected to said feed horn and extending through said tubular means, and

a polarization control motor operatively connected to said rigid sleeve and adapted to rotate same through a selected angle whereby to correspondingly rotate said feed horn relative to the outer housing.

2. The mechanism according to claim 1 with a synchronous transformer operatively connected to said tubular means and responsive to rotation thereof to produce a voltage proportional to angular displacement.

3. Mechanism according to claim 2 with a reference generator operatively connected to said inner housing and responsive to rotation thereof to produce a voltage proportional to angular displacement thereof.

4. Mechanism for nutating a waveguide feed horn adapted to propagate electromagnetic Waves comprising an outer housing,

an inner housing having first and second angularly related and intersecting axes and disposed within and having a forward portion projecting outwardly from one end of the outer housing, said feed horn having a projecting portion extending outwardly from one end of said inner housing, the point of intersection of said axes being adjacent to the end of the horn opposite from the projecting portion thereof,

first antifriction bearings between said housings for supporting the inner housing for rotation about the first axis,

second antifriction bearings between said feed horn and inner housings for supporting the horn on said inner housing for rotation about the second axis,

longitudinally spaced first and second counterweights connected to inner housing on the side of the first axis diametrically opposite from the second axis for dynamically balancing the mechanism when the feed horn is mutating,

a flexible sleeve connected to the feed horn adjacent to the intersection of said axes,

a rigid sleeve connected to said flexible sleeve,

third antifriction bearings rotatably supporting said rigid sleeve in said outer housing for rotation about the first axis,

a flexible radio frequency transmission line connected to the feed horn and extending through said sleeves,

a polarization control motor operatively connected to said rigid sleeve and energizable to displace said rigid and flexible sleeves through a selected angle whereby to correspondingly angular displace the feed horn about the second axis,

a motor operatively connected to said inner housing for rotating the latter about said first axis,

means responsive to angular displacement of the feed device about said second axis for indicating the same, and 7 means responsive to rotation of said inner housing about said first axis for indicating the angular position of the feed device.

References Cited by the Examiner UNITED STATES PATENTS ELI LIEBERMAN, Primary Examiner. 

1. MECHANISM FOR NUTATING A WAVEGUIDE FEED HORN ADAPTED TO PROPAGATE ELECTROMAGNETIC WAVES COMPRISING AN OUTER HOUSING, AN INNER HOUSING DISPOSED WITHIN AND HAVING A FORWARD PORTION PROJECTING OUTWARDLY FROM ONE END OF THE OUTER HOUSING, ANTIFRICTION BEARINGS BETWEEN SAID HOUSINGS FOR SUPPORTING THE INNER HOUSING FOR ROTATION ABOUT A FIRST AXIS RELATIVE TO THE OUTER HOUSING, A MOTOR OPERATIVELY CONNECTED TO THE INNER HOUSING FOR ROTATING THE LATTER ABOUT SAID FIRST AXIS, SAID FEED HORN BEING DISPOSED WITHIN AND HAVING A FORWARD PORTION EXTENDING OUTWARDLY FROM THE FORWARD PORTION OF THE INNER HOUSING, ANTIFRICTION BEARINGS BETWEEN SAID FEED HORN AND INNER HOUSING FOR SUPPORTING THE HORN FOR ROTATION ABOUT A SECOND AXIS RELATIVE TO THE INNER HOUSING, SAID AXES BEING ANGULARLY RELATED AND INTERSECTING AT A POINT ADJACENT TO THE END OF THE HORN OPPOSITE FROM THE FORWARD PORTION THEREOF, COUNTERWEIGHT MEANS CONNECTED TO SAID INNER HOUSING ON THE SIDE OF SAID FIRST AXIS DIAMETRICALLY OPPOSITE FROM THE SECOND AXIS, TUBULAR MEANS CONNECTED TO THE REAR END OF THE FEED HORN AND EXTENDING REARWARDLY THEREFROM COMPRISING A FLEXIBLE SLEEVE AND A RIGID SLEEVE INTERCONNECTED TO THE FLEXIBLE SLEEVE, A FLEXIBLE COAXIAL LINE CONNECTED TO SAID FEED HORN AND EXTENDING THROUGH SAID TUBULAR MEANS, AND A POLARIZATION CONTROL MOTOR OPERATIVELY CONNECTED TO SAID RIGID SLEEVE AND ADAPTED TO ROTATE SAME THROUGH A SELECTED ANGLE WHEREBY TO CORRESPONDINGLY ROTATE SAID FEED HORN RELATIVE TO THE OUTER HOUSING. 